Many drugs and vaccines are administered parenterally by means of injection by medically trained personnel. This involves a first step of reconstitution of the medicament with sterile water for injection, a second step for loading a syringe with an appropriate volume of the dissolved drug, a third step for assembling a sterile needle for injection, a fourth step of administration to the patient by injection, and a final step for safe disposal of the used device. This injection process can be problematic, especially in geographic locations with limited resources. In particular many medicaments require refrigeration in their transport and storage, and failure in maintaining the cold chain can result in significant wastage. More so, the need for reconstitution with sterile water can also be a problem in cases of microbial contamination or use of incorrect reconstitution volumes. Furthermore, the reuse of syringes and needles represents a serious global health problem due to the potential transmission of infectious agents such as Hepatitis or HIV. These problems are specially acute in the administration of vaccines in the developing world, where the World Health Organisation has for long recognised the need for alternative methods (Jodar L. et al. 1998. Revolutionising Immunisations. Gen. Eng. News 18-4).
An alternative method proposed in the administration of medicaments incorporates the administration of solid injectable needles with enough strength and hardness that permits their injection. Once these needles are injected they dissolve or degrade to liberate the medicament. Examples of these injectable needles are illustrated in WO/03023773, and U.S. Pat. No. 6,102,896. If formulated appropriately, injectable needles should avoid the need for refrigeration, reconstitution and use of conventional stainless steel hypodermic needles in the administration of medicaments.
The administration of medicaments in the form of solid injectable needles requires the appropriate devices. Examples of these include those proposed in U.S. Pat. No. 5,542,920 that describes simple devices for the administration of injectable needles which have a sharp tip and are hard enough to penetrate the skin. More so, U.S. Pat. No. 6,102,896 describes an injector for the administration of injectable needles that incorporates breakable tabs that facilitate injection. Injection of injectable needles by means of the devices described in the preceding documents is carried out by direct manual compression action by the user over an actuator. These devices have the inconvenient that the retraction of the injection rod requires the user to liberate the device from the pressure used for the injection, or the removal of the device from immediate contact with the skin. This can result in the injection rod remaining in the body for longer than required and undesirable pain. More so, these devices can be reused or result in accidental third party contamination through accidental contact with the injection rod which has penetrated the patients skin. Furthermore, none of these documents describes methods or designs that facilitate loading the injectable needles into the injectors.
More recently, WO/03023773 proposes injectable needles composed of a solid soluble tip followed by the medicament in the form of a liquid, a paste or a solid. The devices described incorporate a disposable head section and a reusable body. In these devices the user loads the device by means of extending the device and compression of an internal spring. Triggering the device results in the extension of the spring and impact of a piston with another piston attached to the injection rod which pushes forward the injectable needle containing the medicament. The device incorporates a simple mechanism that allows for a small retraction of the injection rod and in its realisation it describes that the injection rod penetrates the skin just enough for the injectable needle to cross the superficial skin. One limitation of the design is that the injectable needles cannot be injected at any significant depth. This can be a serious problem in the administration of medicaments that require a greater injection depth as is the case for most vaccines with optimum depths between 10 mm and 25 mm. Furthermore, the invention focuses on complex devices that can be reused by means of exchangeable head pieces but that presumably have a high economic cost.
In general, previous designs do not allow for simple disposable devices that permit a deep injection and the automatic retraction of the injection rod, to provide efficacious rapid and painless injection while avoiding possible reutilisation of the device and possible third party infection through accidental contact with the injection rod.
It is therefore desirable to have simple disposable devices for the injection of injectable needles containing a medicament at the required depth and that, a) facilitate the manufacture and loading of the injectable needle into the injection device, b) have a mechanism that results in a rapid entry and retraction of the injection rod that pushes forward the injectable needle, and c) that incorporate mechanisms that avoid their reuse and risk of third party contamination.